here i'll use this as an example
y <= -2x + 3
the y-intercept is 3. so the first point you need to plot is (0,3).
the slope is -2. slope is rise/run. so from the point (0,3), go down 2 and over to the right 1, which would be (1,1). plot a point there.
since the inequality is <=, our line is solid. so make a solid line through your two points. shade under the line.